 /*******************************************************************************
  * Copyright (c) 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.internal.intro.impl.util;

 import org.eclipse.core.expressions.EvaluationContext;
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.ui.PlatformUI;

 /*
  * Supplies en evaluation context for filtering intro documents. This is used for
  * resolving variables in enablement expressions.
  */
 public final class IntroEvaluationContext {

     private static final String VARIABLE_PLATFORM = "platform"; //$NON-NLS-1$
 private static final String VARIABLE_WORKBENCH = "workbench"; //$NON-NLS-1$

     private static EvaluationContext context;
     
     /*
      * Returns the evaluation context to use in intro documents.
      */
     public static EvaluationContext getContext() {
         if (context == null) {
             context = new EvaluationContext(null, Platform.class) {
                 public Object getVariable(String name) {
                     if (VARIABLE_PLATFORM.equals(name)) {
                         return Platform.class;
                     }
                     else if (VARIABLE_WORKBENCH.equals(name)) {
                         return PlatformUI.getWorkbench();
                     }
                     return null;
                 }
             };
         }
         return context;
     }
     
     /*
      * Not meant to be instantiated.
      */
     private IntroEvaluationContext() {
     }
 }

